Process and apparatus for making supported catalyst systems for olefin polymerization

ABSTRACT

A process to support a homogeneous catalyst on a porous solid support is performed in two separate zones. In the first zone the solid is contacted, under stirring, with an amount of a catalyst solution lower than the total pore volume of the solid. In the second zone the solid is dried from the solvent while flowing under pneumatic conveying. A loop circulation of solid is established between the two zones, so that the solid is subject to more contacting steps. The process is particularly suitable to support a metallocene-alumoxane polymerization catalyst on a porous prepolymer. The process can be advantageously performed in continuous, thus fitting the needs of an industrial scale production process.

The present invention relates to a method of producing a supportedcatalyst system for use in olefin polymerisation, and to an apparatusused in such a method. Particularly, this invention relates to theproduction of a metallocene-based catalyst supported on a porousmaterial, such as a porous olefin polymer, silica or any other suitableporous material.

It is desirable in the industrial practice to render heterogeneousmetallocene-alumoxane catalysts for, among other reasons, improvingpolymer morphology and reducing reactor fouling. Typically, one or morecatalytic components are supported on a porous support. Usually, themetallocene is deposited on the support from a solution. At the sametime or separately an activator, such as methylalumoxane (MAO), and/oran alkylaluminium compound and/or an ionising activator is/are depositedon the support. The catalyst may be dissolved in one or more liquidmonomers or in a solvent containing one or more monomers. The monomerused is allowed to polymerise during the impregnation of the support orthe evaporation of the solvent.

U.S. Pat. No. 5,625,015 describes a process for depositing a catalyst ona porous solid support by spraying a catalyst solution on the solidmaterial kept under agitation. The volume of solution must be more thanthe total volume of the pores of the treated material, but less than thevolume of solution at which a slurry with the solid would be generated.After this impregnation step, the solvent may be evaporated to allow thecatalytic compounds to deposit on the support.

Kamfjord, Wester and Rytter in Macromol. Rapid Commun. 19, 505–509(1998), describe the preparation of a silica supported metallocene/MAOcatalyst according to the “incipient wetness” method. This methodprovides a route for depositing a dissolved substance onto a solidsupport. The principle of this method is to add only enough of thesolution to fill the pores of the support, in order to allow the soluteto be evenly distributed in the pores of the support. A problem withthis technique is that, by pouring the solution over the support usingthe traditional batch or dropwise technique, a local overwetting mayoccur, especially when the catalyst is prepared on a large scale andwhen the support has a medium-low porosity. The uneven distribution ofthe catalytic system, due to the localised wetting, can affect locallythe heat and mass transfer during the polymerisation generating a poorprocess control and in some cases producing also fines.

The methods according to the prior art improve the distribution of thecatalyst and are suited when the solid support is capable of chemicallybinding the catalytic compound, as it happens when silica is employed.This is not yet sufficient when, as it happens when a polymeric materialis used, the support material has no affinity with the catalyticcompound.

An improved supportation of catalyst components on porous substrates isachieved according to the invention by a process for preparing asupported catalyst comprising the steps of:

-   (a) preparing a catalyst solution comprising a soluble catalyst    component;-   (b) introducing into a contacting vessel:    -   (i) a porous support material in particle form, and    -   (ii) a volume of the catalyst solution not greater than the        total pore volume of the porous support material introduced;-   (c) discharging the material resulting from step (b) from the    contacting vessel and introducing it into an evaporation zone where    it is suspended in an inert gas flow under such conditions that the    solvent evaporates; and-   (d) reintroducing at least part of the material resulting from    step (c) into the contacting vessel together with another volume of    the catalyst solution not greater than the total pore volume of the    reintroduced material.

To maximise the amount of catalyst component(s) deposited on the supportparticles the material resulting from step (d) can be subjected tofurther cycles of steps (c) and (d). The supported catalyst can besuitably recovered after a drying step (c).

In order to ensure a good homogenisation of the system, the contactingvessel is preferably kept under stirring.

A major advantage of the present process is the simultaneousaccomplishment of impregnation and evaporation treatments on the supportparticles in different zones, without the need of discontinuing theimpregnation to evaporate the solvent.

The process can suitably be performed in a loop reactor in which thesupport particles are recirculated and where, in a contacting vessel thesolution(s) of the catalyst components is/are added continuously and inan evaporation zone the solvent is continuously evaporated in order tomaintain a free-flowing solid.

According to a preferred embodiment of the invention, the gas streamused to suspend the solid particles in the evaporation zone is also usedfor pneumatically circulating the solid through the reactor. The soliddischarged from the contacting vessel is entrained by the said gasstream, from which it is separated before or upon being reintroducedinto the contacting vessel. Nitrogen is a preferred inert gas used togenerate the said gas stream and to dry the impregnated solid particles.

The process of the invention can be performed in a semi-continuous or,preferably, in a continuous mode. In the case of semi-continuousoperation, the solid material is loaded into the loop reactor and, afterhaving been contacted with the desired amount of solution within anumber of passages through the contacting vessel and the evaporationzone, it is discharged. The discharging is preferably made from a pointof the loop where the solid has been freed from the solvent, i.e. afterit has left the evaporation zone, while being kept circulating in theloop. In the case of continues operation, the solid is continuously fedat a suitable point, preferably directly into the contacting vessel, andit is withdrawn at any suitable point, preferably where it is free ofthe solvent and more preferably where it comes out from the evaporationzone. Inert gas is continuously fed, preferably at the point ofdischarge of the solid from the contacting vessel and inert gascontaining solvent is withdrawn from any suitable point.

The ratio of the solid recycled in the loop to the solid withdrawn andthe flow of feed solution must be calculated in order to assure asufficient average number of passages of the solid through thecontacting vessel. The average number of passages is preferably above 5,more preferably above 10, and may reach values of 50 and more.

It is not required that all the solvent absorbed by the solid isevaporated in each passage through the evaporation zone. In fact, when aporous prepolymer is used, the solvent besides being typically absorbedin the pores of the particle, it also diffuses into the polymericmaterial, thus causing a swelling thereof. This amount of diffusedsolvent does not prevent fresh solution to enter the pores in asubsequent contacting step, thus it is not necessary to eliminate itbefore the solid is fed again into the contacting vessel. The totalevaporation at this stage would require an unnecessarily long residencetime in the evaporation zone. On the contrary, the solid is generallytotally freed from the solvent when it is discharged from the apparatus.When operations are carried out in a semi-continuous mode, this may beachieved by maintaining the solid in circulation through the apparatusfor a sufficient time after feeding of fresh solution has beenterminated. When the process is carried out continuously, it ispreferred that the apparatus is provided with a secondary evaporationzone, through which the solid is made to flow after having beendischarged from the circulation loop comprising the contacting vesseland the previously mentioned evaporation zone. Since the solutionprovokes the swelling of the solid, this must be taken intoconsideration when calculating the size of the components of theapparatus. For instance, a solid prepolymer containing a residual amountof a solvent such as toluene diffused into the material, after theevaporation step can present an increase of weight, with respect to thedry polymer, of about 8%.

The process according to the present invention allows a uniformdistribution of the catalytic system over the surface area of the porousparticles, which provides an industrially useful supported catalyst withgood morphology, high activity and reduced fouling.

As used herein, “support” means any support material, preferably aporous material such as inorganic oxides, inorganic chlorides andresinous material such as polyolefins or polymeric compounds or anyother organic support material. Particularly preferred support materialsare olefin polymers and prepolymers, generally obtained from aZiegler-Natta catalyst system, and inorganic oxides, such as silica. Inaddition inorganic chlorides, such as magnesium dichloride, can suitablybe used. Generally, the support material is not active in thepolymerisation of olefins. Moreover, it may be either partially ortotally dehydrated.

Preferably the support has an average particle size in the range of fromabout 10 to about 1000 μm, a surface area in the range of from about 1to about 500 m²/g and a porosity in the range of from about 0.1 to about2 ml/g (excluding macropores, i.e. pores with a diameter above 10 μm).The support pore size, in terms of the average diameter of the pores, isgenerally in the range of from about 0.01 to about 2 μm. Typical valuesof porosity for inorganic oxides, such as silica and alumina, are from0.9 to 1.7 ml/g. When a porous prepolymer is used as support material,its porosity is preferably at least 0.3 ml/g. Prepolymers with highervalues of porosity, such as above 0.7 ml/g and even of 1.5 ml/g or more,can advantageously be employed.

The process according to the invention is suitable to prepare supportedpolymerisation catalysts, particularly for olefin polymerisation. Theprocess of the invention is especially suitable for supportingmetallocene-based catalyst systems, such as those described in EP 129368. Other homogeneous catalytic systems that can be supported aremono-cyclopentadienyl catalyst systems such as those described in EP416,815 and EP 420,436. Further homogeneous catalytic systems that canbe supported are those based on late transition metal complexes such asthose described in WO 96/23010.

The catalyst systems to be supported generally comprise an activator. Inthe case of metallocenes, for instance, the activator can be analumoxane or a ionising activator capable of forming an alkylmetallocene cation. Examples of alumoxanes suitable for use according tothe present invention are methylalumoxane (MAO),tetra-(isobutyl)alumoxane (TIBAO),tetra-(2,4,4-trimethyl-pentyl)alumoxane (TIOAO),tetra-(2,3-dimethylbutyl)alumoxane (TDMBAO) andtetra-(2,3,3-trimethylbutyl)alumoxane (TTMBAO). Non limitative examplesof ionising activators are compounds of formula T⁺D⁻, wherein T⁺ is aBroensted acid, able to give a proton and to react irreversibly with aσ-bonded substituent of the metallocene, and D⁻ is a compatible anion,which does not co-ordinate, which is able to stabilise the activecatalytic species originating from the reaction of the two compounds andwhich is sufficiently labile to be removed from an olefinic substrate.Preferably, the anion D⁻ comprises one or more boron atoms. Morepreferably, the anion D⁻ is an anion of the formula BAr⁽⁻⁾ ₄, whereinsubstituents Ar, the same or different from each other, are arylradicals such as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl.Particularly preferred is the tetrakis-pentafluorophenyl borate.Furthermore, compounds of formula BAr₃ can be suitably used.

The supported catalyst may be prepared in a variety of ways. Themetallocene can be dissolved in a solvent either separately from ortogether with the activator and/or the monomer and vice versa. Thedeposition of the catalytic system components on the support can be madein any possible order. Suitable solvents for preparing ametallocene-based catalyst solution are liquid aliphatic or aromatichydrocarbons, such as toluene.

The ratio of the total volume of the catalyst (in the sense of catalyticsystem) solution employed in the process of the invention to the totalpore volume of the support may be in the range of from about 4 to about20.

The mole ratio of the metal of the activator to the transition metal ofthe metallocene is in the range of ratios between 1:1 and 1000:1, morepreferably 20:1 to 500:1, and most preferably 50:1 to 250:1. If theactivator is an ionising activator, the mole ratio of the metal of theactivator to the transition metal is preferably in the range of ratiosbetween 0.3:1 and 3:1.

When the catalyst is a metallocene and the activator is an alumoxanesuch as methylalumoxane, according to a preferred embodiment the processis carried out in at least two phases: in a first phase all themetallocene compound together with part of the alumoxane is contactedwith the support, and in a second phase the remaining amount ofalumoxane is contacted with the solid support. As an example ¾ of thetotally employed amount of alumoxane is employed in the first step andthe remaining ¼ in the second.

If the catalyst system comprises two different metallocene compounds,they may suitably be contacted separately in two different phases: in afirst phase one metallocene is contacted with the solid support, and inthe second phase the other metallocene is contacted with the solidsupport. As an example, a solution comprising the first metallocene andabout half of the totally employed amount of alumoxane is employed inthe first step, and a solution comprising the other metallocene andabout half of the totally employed amount of alumoxane is employed inthe second step. Or better, the alumoxane can be contacted with thesolid support, part along with one metallocene in the first phase, partalong with the other metallocene in the second phase, and part in afurther contacting phase. As an example, a solution comprising the firstmetallocene and about ⅜ of the totally employed amount of alumoxane isemployed in the first step, a solution comprising the other metalloceneand about ⅜ of the totally employed amount of alumoxane is employed inthe second step and a solution containing the remaining alumoxane in afurther contacting step.

The contacting vessel is preferably provided with means for mixing thesupport, while the solution is introduced, in order to avoid overwettingof the support and the agglomeration of the particles. Any suitablemeans of mixing or agitation may be used. Such means include mixers andagitators with one or more extending arms. The arms may be of any shape,length and orientation. The means for mixing the support and thestirring conditions must be chosen so as to minimise the breakage orfracturing of the support, in order to avoid considerable generation offines. The catalyst solution may be poured into the contacting vessel bymeans of a dosing pump or any other possible system able to dose aliquid. There is no need of spraying the solution or of producing a mistor fog or aerosol. The solution may enter the vessel through one or morepoints; small pipes can be used to introduce the solution into thevessel. The position of the feed point(s) into the contacting vessel maybe over or under the solid bed. Means for discharging the solid with acontrolled flow rate are necessary to control the dosing rate of thesolution. In fact the ratio of the liquid flow rate to the recirculatingsolid flow rate is set in order to just fill the pore volume and tomaintain a free-flowing solid. Any means for dosing solid particles,such as a screw or a cup, are suitable. The means for discharging thesupport must be chosen so as to reduce as most as possible the breakageof the support.

The impregnation of the support in the contacting vessel as well as theevaporation of the solvent in the evaporation zone may be carried out atany pressure, over any period of time and at any temperature, providedthe temperature of the solution and/or support is maintained such thatthe components of the catalyst solution do not decompose and thesolution does not solidify.

According to a preferred embodiment, the contacting vessel is shaped asa vertical column through which the solid flows downward in a packedform. The contacting vessel as well as the evaporation zone arepreferably equipped with a thermostatic jacket, in order to carry outthe impregnation and the evaporation of the solvent at the desiredtemperature. It has to be noted that the process of the presentinvention allows a separate regulation of the temperature upon thecontacting and the evaporation, so that an optimal temperature can bechosen for both the process steps. The evaporation zone can be a pipe ormore pipes arranged in parallel. A possible scheme of the process of theinvention is illustrated in FIG. 1. The porous support is loaded intothe contacting column 1, from which it is discharged by a screw valve 3and is pneumatically conveyed through the column 2 and finallyrecirculated to the column 1 by means of an inert gas stream introducedby pipe 4. The catalyst solution is fed by means of a dosing pump 8 intocolumn 1 where it is contacted with the porous support. A mechanicalstirrer 5 is used to improve the contact between the liquid and theporous particles. The ratio between the recirculating solid and thepoured liquid is lower than that needed to fill the pores, so thatnowhere in the column local excess of liquid can be generated. Thevolume of solution fed into the contacting vessel is preferablycomprised between 20 and 80%, more preferably it is from 50 to 60% ofthe total pore volume of the solid fed into the contacting vessel,especially when continuous operation is performed in an industrial-scaleplant. The column 2 is heated in order to evaporate the solvent that isremoved by the inert gas flow. The upper part 7 of column 1 is used asseparator of the solid from the gas containing the evaporated solvent.Alternatively, it is possible to separate the solid from the gas streambefore it enters the column 1 by means of a cyclone or any othersuitable device. The gas stream of inert gas and solvent vapours goes toa condensation zone 6 to separate the solvent from the inert gas, whilethe separated solid flows again through column 1 where it is contactedwith another volume of catalyst solution. Columns 1 and 2 are bothequipped with a thermostatic jacket. The preparation of the supportedcatalyst is completed when all the components of the catalytic systemhave been deposited on the support. It is possible to deposit all thecatalyst components together or in subsequent impregnation processes,depending on the characteristics of the catalyst system. If the catalystsystem does not undergo decay after contacting with all the catalystcomponents, it is generally preferred to deposit all the catalystcomponents together. The dried solid can be unloaded as it is or it canbe prepolymerized using one or more alpha-olefins in gas-phase, eitherin the same equipment or in a different reactor. The prepolymerisationmay also be carried out in slurry phase. When a metallocene is used as acatalyst component, the prepolymerisation may be particularly advisablein order to prevent the successive leaking of the catalyst, which cangenerate fouling during the polymerisation process.

In case of continuos operation, the solid is continuously fed to column1 by any suitable dosing device and it is continuously withdrawngenerally at a point between the exit from column 2 and thereintroduction into column 1. Means for separating the withdrawn solidfrom the accompanying gas must be provided. If the whole recycle streamundergoes separation before reintroduction into column 1, it issufficient to discharge a part of the separated solid.

According to another aspect, the present invention relates to anapparatus comprising a contacting vessel 1 equipped with a mechanicalstirring device 5 and means 3 for discharging a solid in particle formfrom vessel 1, a line 4 for introducing gas at a point after thedischarging means 3, an evaporation zone 2, preferably jacketed forthermostatic control, means 8 for introducing a catalyst solution intothe vessel 1, means 7 for separating the particulate solid from the gasstream. Preferably, a condenser 6 is also provided to separate thesolvent from the gas stream coming from the means 7 for separating thesolid from the gas stream. Also the contacting vessel 1 is preferablyjacketed for temperature control.

If the apparatus is used for continuous operation, means forcontinuously introducing the solid into the vessel 1 and for withdrawingsolid after the evaporation zone 2 must also be provided. According to apreferred embodiment the apparatus is also provided with a furtherevaporation zone placed downstream of the point of discharge of thesolid. The following examples will further illustrate the presentinvention without limiting its scope.

EXAMPLES

Characterisations

POROSITY: determined by immersing a known quantity of the sample in aknown quantity of mercury inside a dilatometer and then graduallyincreasing the mercury pressure hydraulically. The pressure ofintroduction of the mercury into the pores is function of the porediameter. Measurements were effected using a “Porosimeter 2000 series”from Carlo Erba. The porosity, pore distribution and surface area werecalculated from the data of decrease of the volume of mercury and fromthe values of the applied pressure.

MELT INDEX “L”: ASTM-D 1238, method L.

INTRINSIC VISCOSITY: in tetrahydronaphtalene at 135° C.

BULK DENSITY: DIN-53794.

AVERAGE PARTICLE SIZE (APS): determined with a method based on theprinciple of optical diffraction of monochromatic laser light with the“Malvern Instr. 2600” apparatus. The mean size is stated at P50.

Preparation of the Supported Catalysts

Supported catalysts were prepared using the equipment illustrated inFIG. 1 operating in a semi-continuous way. The flow of the solid throughthe apparatus was regulated in order to assure an average number ofpassages through the contacting vessel between 10 and 30.

Example 1

Under nitrogen, 280 ml of 100 g/l methylalumoxane solution in toluenewas added to 1.9 g of rac-CH₂(3-tert-butyl-1-indenyl)₂ZrMe₂ to form thecatalyst solution. Separately, 135 g of a porous polyethylene prepolymer(pore volume 0.335 ml/g excluding macropores, APS 152 μm) obtained froma Ziegler-Natta catalyst, previously steamed to deactivate the catalystresidues and then dehydrated in a stream of flowing nitrogen at 110° C.,was loaded in the equipment of FIG. 1. The jacket temperature of column1 was set to 55° C. and that of column 2 was set to 110° C. The agitatorof column 1 was activated and recirculation of the solid in the loopreactor was initiated by opening the nitrogen flow through column 2. Thedosing of the solution was initiated by activating the dosing pump. Allthe solution was added to the support in 2 hours; at the end of thistime, the support was maintained in recirculation for 15 minutes withoutadding any other liquid to eliminate the last traces of solvent. Duringall the addition time, the support was finely divided and free-flowing.The analysis of the final catalyst was 6.3 wt. % Al and 0.2 wt. % Zrwith an Al/Zr molar ratio of 106.

Example 2

Using the procedure of example 1, a solution was prepared by adding 200ml of the 100 g/l methylalumoxane solution to 1.9 g ofrac-CH₂(3-tert-butyl-1-indenyl)₂ZrMe₂. 135 g of the same polyethyleneprepolymer previously treated as described in example 1 were loaded inthe same equipment. The jacket of the two columns was heated at thedesired temperature and the solid was fluidised in the circulatingreactor. The solution was added to the support in 90 minutes.Immediately after other 80 ml of the 100 g/l MAO solution were added tothe supported catalyst to reach the desired amount of supportedmethylalumoxane. Once finished the addition of the solution, the solidwas circulated for 15 minutes to eliminate the traces of the solvent.The unloaded supported catalyst had the following analysis: 6.9 wt. % Aland 0.22 wt. % Zr with an Al/Zr molar ratio of 106.

Example 3

Using the procedure of example 1, a solution was prepared under nitrogenadding 7000 ml of a methylalumoxane solution 100 g/l in toluene to 60 gof rac-dimethylsilylenbis(2-methyl-4-phenyl-1-indenyl)ZrCl₂. 2100 g of apolypropylene prepolymer (porosity 0.386 g/ml excluding macropores, APS142 μm), previously steamed and dehydrated were loaded in an equipmentsimilar to that of example 1 but of larger scale. The jacket of thecolumn 1 was heated to 50° C., that of column 2 was heated to 110° C.,and the solid was recirculated into the apparatus. The solution wasadded to the support by dosing the liquid with a dosing pump trough 4different feed points in order to better distribute the liquid andimprove the contact between the liquid and the porous solid. Thesolution was fed in 3 hours, after this time the catalyst wasrecirculated for extra 30 minutes to remove the last traces of solvent.The unloaded supported catalyst had the following composition: 8.5% wt.Al and 0.28% wt. Zr with an Al/Zr molar ratio of 102. Part of theunloaded catalyst was transferred to a fluidised bed reactor to beprepolymerised with ethylene. The polymerisation was performed at 50°C., 120 kPa, in a stream of propane/ethylene (10% molar fraction ofethylene) for 2 hours to obtain a productivity of 1.1 g/g. Thecomposition of the prepolymerised catalyst was 7.65% wt. Al and 0.26%wt. Zr.

Example 4

Under nitrogen, the cocatalyst solution was prepared by adding 40 ml ofpure tri-iso-octylaluminium to 200 ml of a methylalumoxane solution 100g/l in toluene and let to react for 30 minutes. This solution was addedto 1.95 g of (Me₃SiCP)₂ZrCl₂ to obtain the catalytic solution. Using theprocedure described in example 1, 250 g of a polyethylene prepolymerwere loaded in the same equipment. The jacket of column 1 was heated to50° C. and that of column 2 to 90° C. The solution was dosed in 2 hoursto the recirculating support. The supported catalyst was circulated for15 more minutes to completely dry it. The obtained catalyst had thefollowing analysis: 2.7% wt. Al and 0.14% wt. Zr with an Al/Zr molarratio of 65.

Polymerisations

Examples 5–7

Catalyst samples as prepared in examples 1–3 were used for propylenepolymerisations as described below. Batch polymerisations were carriedout in a 4 l stirred autoclave. 1200 g of liquid monomer were loaded at30° C., followed by 1.16 ml of a TEAL solution 100 g/l in hexane used asa scavenger. The polymerisation was started by injecting the catalystinto the autoclave at 30° C., by means of nitrogen overpressure, thenthe temperature was raised up to 60° C. in 10 minutes and maintained for2 hours. The polymerisation was stopped by venting and cooling thereactor. No significant fouling was observed. The product obtained wascollected and dried in an oven flushed with nitrogen at 70° C. for 3hours. The polymerisation data and properties of the polymer samples arereported in Table 1.

Example 8

A sample of catalyst as prepared in example 4 was used for ethylenepolymerisation as described below. A 4 l stirred autoclave was used. Thecatalyst was suspended in 5 ml of hexane and charged into the autoclavecontaining 1.5 l of liquid hexane at 30° C., the autoclave waspressurised with ethylene at a total pressure of 1100 kPa. 1.16 ml of aTEAL solution 100 g/l in hexane was used as scavenger and fed into thereactor before adding the catalyst and starting the polymerisation. Thetemperature was raised up to 80° C. in 10 minutes and maintained for 2hours. Finished the polymerisation the reactor was cooled and vented. Nosignificant fouling was observed. The product obtained was collected anddried in an oven flushed with nitrogen at 70° C. for 3 hours. Thepolymerisation data and properties of the polymer samples obtained arereported in Table 1.

TABLE 1 EXAMPLE 5 6 7 8 Catalyst ex. 1 ex. 2 ex. 3 ex. 4 Pressure (kPa)2800 2800 2800 1100 Temperature (° C.) 60 60 60 80 Monomer C₃H₆ C₃H₆C₃H₆ C₂H₄ Productivity (g/g) 780 1000 3000 690 Melt index “L” 50.4 61<0.1 — (g/10 min) Intrinsic viscosity (dl/g) — — — 8.8 Melting point (°C.) 151.6 156 146.8 — Bulk density (g/ml) 0.381 0.420 0.370 0.374 APS(μm) 1649 1639 2160 1374

1. A process for preparing a supported catalyst comprising the steps of:(a) preparing a catalyst solution comprising a soluble catalystcomponent; (b) introducing into a contacting vessel: (i) a poroussupport material in particle form, and (ii) a volume of the catalystsolution not greater than the total pore volume of the porous supportmaterial introduced; (c) discharging the solid material resulting fromstep (b) from the contacting vessel and introducing it into anevaporation zone where it is suspended in an inert gas flow under suchconditions that the solvent evaporates; and (d) reintroducing at leastpart of the material resulting from step (c) into the contacting vesseltogether with another volume of the catalyst solution not greater thanthe total pore volume of the reintroduced material.
 2. The processaccording to claim 1 wherein the material resulting from step (d) issubjected to further cycles of steps (c) and (d).
 3. The processaccording to claim 1 wherein the contacting vessel is kept understirring.
 4. The process according to claim 1 wherein the operations arecarried out continuously and wherein the porous support material iscontinuously fed and the solid material resulting from step (b) iscontinuously discharged at any suitable point where the circulatingsolid flows, the inert gas is continuously fed at a point subsequent tothe point of discharge of the solid material from the contacting vessel,and the inert gas containing solvent is withdrawn from any suitablepoint.
 5. The process according to claim 1 wherein the volume of thecatalyst solution fed into the contacting vessel is from 20 to 80% ofthe total pore volume of the porous support material fed into thecontacting vessel.
 6. The process according to claim 5 wherein thevolume of the catalyst solution fed into the contacting vessel is from50 to 60% of the total pore volume of the porous support material fedinto the contacting vessel.
 7. The process according to claim 1 whereinthe contacting vessel is a column jacketed for temperature control andprovided with a mechanical stirring device.
 8. The process according toclaim 1 wherein the evaporation zone is a pipe provided with a jacketfor temperature control.
 9. The process according to claim 1 wherein theinert gas is nitrogen.
 10. The process according to claim 1 wherein thecontacting vessel is equipped with a screw valve for the withdrawal ofthe solid material.
 11. The process according to claim 1 wherein thecatalyst solution comprises a metallocene compound.
 12. The processaccording to claim 11 wherein the catalyst solution comprises analuminium alkyl compound.
 13. The process according to claim 1 whereinthe porous support material is a porous polyolefin prepolymer.
 14. Theprocess according to claim 13 wherein the prepolymer has a porosity ofat least 0.3 ml/g.
 15. The process according to claim 14 wherein theprepolymer has a porosity of at least 1.5 ml/g.
 16. The processaccording to claim 11 wherein the solvent of the catalyst solution is aninert hydrocarbon solvent.
 17. The process according to claim 12 whichis carried out in a first phase when all the metallocene compoundtogether with part of the aluminium alkyl compound is contacted with theporous support material, and in a second phase when the remaining amountof aluminium alkyl compound is contacted with the porous supportmaterial.
 18. The process according to claim 11 wherein two differentmetallocene compounds are used, the said process being carried out in afirst phase when one metallocene is contacted with the porous supportmaterial, and in the second phase when the other metallocene iscontacted with the porous support material.
 19. The process according toclaim 18 wherein an aluminium alkyl compound is contacted with theporous support material, part along with one metallocene in the firstphase, part along with the other metallocene in the second phase, andpart in a further contacting phase.
 20. An apparatus comprising acontacting vessel, equipped with a mechanical stirring device and meansfor discharging a solid in particle form from the contacting vessel, aline for introducing gas at a point after the discharging means, anevaporation zone, means for introducing a catalyst solution into thecontacting vessel, and means for separating the particulate solid fromthe gas stream.
 21. The apparatus according to claim 20, wherein thecontacting vessel and the evaporation zone are jacketed for temperaturecontrol.
 22. The apparatus according to claim 20 wherein a condenser isprovided to separate the solvent of the catalyst solution from the gasstream coming from the means for separating the solid from the gasstream.
 23. The apparatus according to claim 20 which is provided withmeans for continuously introducing the solid into the contacting vesseland for continuously discharging the solid at a point where it has comeout from the evaporation zone.
 24. The apparatus according to claim 23which is provided with a further evaporation zone placed downstream ofthe point of discharge of the solid.